MOSCOW (Dow Jones)--Russia will extend its ban on grain exports until after next year's harvest has been collected, Prime Minister Vladimir Putin said Thursday in an announcement that caught many in the industry off guard.

"It is necessary to note that we will be able to end the export ban only after next year's harvest is gathered and the picture regarding grain balances becomes clearer," Putin said.

In a bid to reign in surging grain prices after Russia's worst drought in decades destroyed more than a quarter of its harvest, the country last month announced an export ban that was ...